## TeX

TeX was the first language to get its own StackExchange site.

(Note that we will show examples in plain TeX mostly; if any example is to be compiled using LaTeX, it will be clearly stated.)

## 6 `\relax`

TeX is one of the languages that have its own "do nothing" action. However, `\relax` is more than just that, and this is related to the fact that it is an _expansion language_: All macros are expanded, and in some contexts, executed. The power of `\relax` is that it is executed to nothing, but it cannot be expanded, i.e., it survives any expansion unmodified. This in turn is one of the strenghts (and treats at the same time, especially for newcomers) of TeX.

## 5 `X\bye`

A minimal document that compiles producing an output; we get a page with a 10-point "X" at the top and a centred page number "1" at the bottom. _... "X," said Tom, and added, leaving: "Bye!"_

## 4 `\bye`

When you say "bye" to TeX, it finishes the document; namely it closes the current paragraph if any is open, ships out the last page, and ends. Without this command, no document can be successfully produced.

## 3 `$a$`

Prints the mathematical symbol "a", that can stand for instance for a variable, function or a constant. Without the dollars, it would be the text symbol "a"; it is necessary to distinguish these two!

## 2 `<endline><endline>`

Two consecutive ends of line finish a paragraph. (One end of line behaves like a space.)

## 1 `%`

The percent sign starts a comment; the comment runs until the end of line, and eats the end of line together with leading whitespace on the next line.